1. Field of the Invention
The present invention relates to a lens barrel unit provided with a lens barrier, and a camera incorporating the lens barrel unit.
2. Description of the Related Art
Conventionally, a compact camera, such as a lens shutter camera, is known which is equipped with a lens cap that can be attached and detached to and from the front of a photographic lens. The lens cap is mounted on the camera when the camera is not used, so as to protect the photographic lens or cut external light.
Further, in recent years, many cameras have come to employ a lens barrier provided in a portion of a camera body thereof or of a lens barrel instead of a lens cap, and drivingly control the lens barrier by a barrier driving means provided in the camera body.
In the following, a lens barrel unit provided with the above-mentioned lens barrier will be described with reference to FIG. 5. FIG. 5 is an exploded perspective view of the conventional lens barrel unit with a lens barrier.
As shown in FIG. 5, the lens barrel unit with a lens barrier includes a lens barrel 102. The lens barrel 102 holds a lens 101 and a barrier base plate 103 as a base for mounting component parts constituting a barrier mechanism. Further, the lens barrel 102 incorporates a lens barrier 104 for protecting the lens 101, and a driving mechanism for the lens barrier 104.
The barrier base plate 103 has an annular shape. The barrier base plate 103 has a pair of engaging shafts 103a formed thereon at locations diametrically opposed in a direction orthogonal to an optical axis, a pair of hooks 103b formed thereon at locations diametrically opposed in the direction orthogonal to the optical axis, and a pair of sectoral cutouts 103c formed in a periphery thereof at locations diametrically opposed in the direction orthogonal to the optical axis.
The lens barrier 104 is comprised of a pair of blade members 104A having the same shape, and the blade members 104A are arranged point-symmetrically with respect to the optical axis. Each blade member 104A is formed therein with an engaging hole 104a serving as the center of rotation of the blade member, a hook 104b for a closing spring 105, and a driving pin 104c disposed at a location away from the engaging hole 104a. 
Each engaging shaft 103a extending from the barrier base plate 103 is fitted through an associated one of the engaging holes 104a of the respective blade members 104A, whereby the blade members 104A are supported in a manner rotatable about the respective associated engaging shafts 103a. 
Each closing spring 105 is formed by a tensile spring. The closing spring 105 has one end thereof hooked to an associated one of the hooks 104b and the other end thereof hooked to an associated one of the hooks 103b of the barrier base plate 103. The blade members 104A are urged by the respective closing springs 105, for rotation about the respective associated engaging shafts 103a in a counterclockwise (hereinafter abbreviated as CCW) direction as viewed in FIG. 4. In short, the barrier 104 constantly receives a turning force acting in the closing direction.
The driving pin 104c of each blade member 104A is inserted through an associated one of the cutouts 103c of the barrier base plate 103 and extends toward a barrier driving ring 107, described hereinafter.
Further, the lens barrel 102 holds a barrier cover 106 such that the barrier cover 106 and the barrier base plate 103 define therebetween a working space for the blade members 104A constituting the lens barrier 104.
The barrier driving ring 107 is disposed between the lens barrel 102 and the barrier base plate 103, for opening and closing the lens barrier 104. The barrier driving ring 107 is supported by the lens barrel 102 in a manner rotatable about the optical axis. The barrier driving ring 107 is formed with a pair of contact parts 107a at diametrically opposite locations, a hook 107b, and an engaging part 107c projecting toward the lens barrel 102.
Each contact part 107a comes into contact with the driving pin 104c of an associated one of the blade members 104A during rotation of the barrier driving ring 107 to urge the lens barrier 104 in the opening direction. When the contact parts 107a urge the driving pins 104c of the respective associated blade members 104A, the driving pins 104c are pivotally moved about the respective engaging holes 104a. In other words, the blade members 104A constituting the lens barrier 104 are pivotally moved about the respective engaging holes 104a. This causes the lens barrier 104 to form or open a light passing port for the lens 101.
An opening spring 108 formed by a tensile spring has one end thereof hooked to the hook 107b and the other end thereof hooked to a hook 102a formed inside the lens barrel 102. The opening spring 108 constantly urges the barrier driving ring 107, for rotation about the optical axis in a clockwise (hereinafter abbreviated as CW) direction as viewed in FIG. 4.
When the lens barrel unit is not in use, the engaging part 107c is held in contact with an action member, not shown. The action member acts to apply a CCW turning force to the barrier driving ring 107. In doing this, the action member acts on the barrier driving ring 107 against the urging force generated by the opening spring 108, whereby the barrier driving ring 107 is rotated in the CCW direction. As the barrier driving ring 107 is thus rotated, the contact parts 107a move away from the respective associated driving pins 104c. As a consequence, the blade members 104A of the lens barrier 104 are brought into a closed state by the respective closing springs 105. Thus, the lens barrier 104 closes the light passing port for the lens 101 so as to protect the lens 101.
When the lens barrel unit is in use, the positional relationship between the action member and the engaging part 107c is changed such that the action member and the engaging part 107c are disengaged from each other. As a consequence, the barrier driving ring 107 is rotated in the CW direction by the opening spring 108, whereby the contact parts 107a are brought into contact with the respective driving pins 104c. This causes a CW turning force to act on the blade members 104A. At this time, the urging force of the opening spring 108 acting on the barrier driving ring 107 is stronger than the urging force of the closing springs 105 acting on the blade members 104A, so that the blade members 104A are opened. Thus, the light passing port for the lens 101 is opened by the lens barrier 104.
In the above described way, the lens barrier 104 which automatically opens and closes depending on whether or not the lens barrel unit is in use enables the user to use an image pickup apparatus or camera having the lens barrel unit without considering whether to open or close the lens barrier 104, which contributes to improvement of the user-friendliness of the image pickup apparatus (see e.g. Japanese Laid-Open Patent Publications (Kokai) Nos. 2004-069991 and 2004-045744).
However, in the above described conventional lens barrel unit with a lens barrier, since the pair of sectoral cutouts 103c through which the respective driving pins 103c are inserted are formed in the barrier base plate 103, external dirt or dust can enter the working space for the barrier driving ring 107 via the cutouts 103c, which can make the lens barrel unit faulty. Further, it is difficult to provide a waterproof or drip-proof function for the image pickup apparatus having the lens barrel unit with a lens barrier.